Generally, a reciprocating compressor sucks, compressed, and then discharges refrigerant gas by linearly reciprocating a piston in a cylinder. The compressor is divided into a reciprocating compressor and a linear compressor according to a driving method of the piston.
In the reciprocating compressor, a crankshaft is coupled to a rotary motor and a piston is coupled to the crankshaft, thereby converting a rotation force of the rotary motor into a reciprocation force.
In the linear compressor, a piston connected to a mover of a linear motor is linearly moved.
The linear compressor is not provided with a crank shaft for converting a rotation motion into a linear motion thus not to have a frictional loss due to the crank shaft, thereby having a higher compression efficiency than a general compressor.
When the linear compressor is applied to a refrigerator or an air conditioner, a compression ratio of the linear compressor is varied by varying a voltage applied to a motor inside the linear compressor. Accordingly, a cooling capacity of the refrigerator or the air conditioner is controlled.
When the linear compressor is applied to a refrigerator or an air conditioner, a compression ratio of the linear compressor is varied by varying a stroke voltage applied to the linear compressor. Accordingly, a cooling capacity of the refrigerator or the air conditioner is controlled. Herein, the stroke denotes a distance between an upper dead point of the piston and a lower dead point of the piston.
The related art linear compressor will be explained with reference to FIG. 1.
FIG. 1 is a block diagram showing a driving controlling apparatus for a linear compressor in accordance with the related art.
As shown in FIG. 1, the related art driving controlling apparatus for a linear compressor comprises a current detecting unit 4 for detecting a current applied to a motor (not shown) of the linear compressor 6; a voltage detecting unit 3 for detecting a voltage applied to the motor of the linear compressor 6; a stroke calculating unit 5 for calculating a stroke estimation value of the linear compressor based on the detected current, the detected voltage, and a parameter of the motor; a comparing unit 1 for comparing the calculated stroke estimation value with a preset stroke command value, and outputting a difference value therebetween; and a stroke controlling unit 2 for controlling a turn-on period of a triac (not shown) serially connected to the motor based on the difference value so as to vary a voltage applied to the motor, and thereby controlling a stroke of the linear compressor 6.
Hereinafter, an operation of the driving controlling apparatus for a linear compressor will be explained with reference to FIG. 1.
The current detecting unit 4 detects a current applied to a motor (not shown) of the linear compressor 6, and outputs the detected current to the stroke calculating unit 5.
The voltage detecting unit 3 detects a voltage applied to the motor of the linear compressor 6, and outputs the detected voltage to the stroke calculating unit 5.
The stroke calculating unit 5 calculates a stroke estimation value (X) of the linear compressor by substituting the detected current, the detected voltage, and a parameter of the motor into a following equation 1. Then, the stroke calculating unit 5 applies the calculated stroke estimation value (X) to the comparing unit 1.
                    X        =                              1            α                    ⁢                      ∫                                          (                                                      V                    M                                    -                  Ri                  -                                      L                    ⁢                                                                                  ⁢                                          i                      _                                                                      )                            ⁢                              ⅆ                t                                                                        Equation        ⁢                                  ⁢        1            
The R denotes a resistance of the motor, the L denotes an inductance of the motor, the α denotes a constant of the motor, the VM denotes a voltage applied to the motor, the i denotes a current applied to the motor, and the ī denotes a variation ratio of the current applied to the motor according to time. That is, the ī is a differential value of the i (di/dt).
The comparing unit 1 compares the stroke estimation value with the stroke command value, and applies a difference value therebetween to the stroke controlling unit 2.
The stroke controlling unit 2 varies a voltage applied to the motor of the linear compressor 6 based on the difference value, thereby controlling the stroke of the linear compressor 6.
FIG. 2 is a flowchart showing a method for controlling an operation of a linear compressor in accordance with the related art.
Referring to FIG. 2, a stroke estimation value obtained by the stroke calculating unit 5 is applied to the comparing unit 1 (S1). Then, the comparing unit 1 compares the stroke estimation value with a preset stroke command value (S2), and outputs a difference value therebetween to the stroke controlling unit 2.
When the stroke estimation value is smaller than the stroke command value, the stroke controlling unit 2 increases a voltage applied to the motor so as to control a stroke of the linear compressor (S3). On the contrary, when the stroke estimation value is larger than the stroke command value, the stroke controlling unit 2 decreases the voltage applied to the motor (S4).
Herein, the voltage applied to the motor is increased or decreased by controlling a turn-on period of a triac (not shown) electrically connected to the motor.
The stroke command value is varied according to a size of a load of the linear compressor. More concretely, when the load is large, the stroke command value is increased thus to increase the stroke of the piston, thereby preventing decrease of a cooling capacity.
On the contrary, when the load is small, the stroke command value is decreased thus to decrease the stroke of the piston, thereby preventing increase of the cooling capacity and preventing a collision between the piston and the cylinder due to an over stroke.
In the related art method for controlling an operation of a linear compressor, a stroke estimation value of the linear compressor is calculated based on a parameter of a motor, a resistance and a reactance. Then, a stroke control is performed based on the stroke estimation value.
However, when the stroke estimation value is calculated, an error occurs according to a deviation of the parameter and each component thus not to precisely perform the stroke control. Accordingly, the piston is not placed to TDC=0, thereby degrading a reliability of the apparatus.